Piston ring facings

ABSTRACT

This invention covers piston rings, including compression and oil control rings for internal combustion engine pistons, having a bearing face coated with a hard coating, particularly exhibiting good scuff-resistance comprising a zirconium oxide base coating. The coating is preferably a plasma jet applied coating formed in situ on the bearing face.

United States Patent 1191 Prasse et al.

[ PISTON RING FACINGS [75] Inventors: Herbert F. Prasse, St. Louis; Harold E. McCormick, Ballwin, both of Mo.

[73] Assignee: Ramsey Corporation, St. Louis, Mo. [22]. Filed: Oct. 12, 1971 [21 Appl. No.1 188,482

Related US. Application Data [62] Division of Ser. No. 36,143, May ll, I970, Pat. No.

52 Us. (:1. .Q 277/235 A, 29/1565 R 51 1111.01 Fl6j 9/00 [58] Field oi s $51 1 :l277/2 3 5 235 5,236, 23 1 235 1 A; 117/1052, 93.1;29/l56.6

[56] 1 References Cited 7 UNITED STATES PATENTS 3,560,006

2/1971 Watanabe 277/235 A Feb. 26, 1974 3,310,423 3/1967 lngham ..'117/105.2 3,481,715 12/1969 Whalen et a] 277/235 A Primary ExaminerLouis R. Prince Assistant Examiner-Robert 1. Smith Attorney, Agent, or Firm-Hill, Sherman, Meroni, Gross & Simpson 57 ABSTRACT This invention covers piston rings, including compression and oil control rings for internal combustion engine pistons, having a bearing face coated with coating, particularly exhibiting good scuff-resistance comprising a zirconium oxide base coating.'-The coatin situ on the bearing face.

ing is preferably a plasma jet applied coating formed 4 Claims, 6 Drawing Figures PISTON RING FACINGS This is a division of application Ser. No. 36,143, filed May II, 1970 and now US. Pat. No. 3,697,091.

BACKGROUND OF THE INVENTION l. Field of the Invention This invention pertains to the piston ring'art and to the provision of bearing faces on piston rings. The invention particularly deals with plasma jet applied coatings and piston rings which exhibit the desired strength, wear-resistance and scuff-resistance.

,2. Description of the Prior Art It is known that piston rings, including compression rings and oil control rings, must be coated with a hard facing metal in order that they demonstrate long-lasting wear.

Suitable piston rings must also demonstrate other desirable properties for passable performance. For example, the coating must have a sufficiently high melting point and high particle hardness. In addition, the coating must be porous enough to allow. it to carry a lubricant on the surface of the coating, thus imparting good scuff-resisting properties. Other properties which should be present include sufficient bond strength between the coating and the basic ring material, and a relatively low coefficient of expansion.

Two of the most important properties are sufficient I hardness to exhibit proper wear and good scuff- SUMMARY OF THE INVENTION The present invention provides coated piston rings which show relatively low wear rates, coupled with the desired high degree of scuff-resistance. The rings of this invention have their bearing facecoated with a hard coating exhibiting good scuff-resistancenThe coating comprises a zirconium oxide-base coating. These coatings are most preferably applied by means of a plasma jet spraying technique, whereby the coating is formed in situ on the bearing face.-If desired, the piston ring bearingface may also contain an underlying bond coat which most preferably comprises anic'kel-aluminide coating. Such underlying coat is particularly useful when the coated rings are used in heavy duty engines.

In accordance with apreferred embodiment of the invention, ferrous metal compression rings composed of conventionally cast nodular iron of about 3-l2 percent carbon content by weight, thin rai] rings foroil control assemblies composed of carbon steel such as S.A.E. I070, and the like base metal rings, are coated with a plasma jet stream comprising a powder composed primary of zirconium oxide.

The plasma jet utilizes a fuel gas preferably composed of a mixture of nitrogen or argon with or without hydrogen. The compression rings are preferably peripherally grooved and the groove is filledwith an alloy resulting from the plasma jet application of the zirconium oxide powder. The powder is vaporized and deposited in the ring groove as an in situ formed coating.

It is therefore an object of this invention to provide improved piston rings with hard-faced bearing surfaces exhibiting good wear and scuff-resistance.

Another object of the invention is to provide piston rings having plasma jet applied zirconia coatings.

A specific object of the invention is to provide an engine piston ring having an annular groove thereon filled with a layer of a zirconium oxide coating which has sufficient porosity to allow it to carry a lubricant.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings,

all variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which the following detailed description of the annexed sheet of drawings by way of preferred example illustrate several embodi- I ments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 isa side elevational view, with parts in cross section, of an engine piston and cylinder assembly, wherein the piston has ring grooves equipped with compression and oil control rings each having a bearing face engaging the cylinder which is composed of one or more in situ formed plasma jet applied coatings, according to this invention;

FIG. 2 is an enlarged fragmentary cross sectional view of the top compression ring in the piston on FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The piston and cylinder assembly 10 of FIG. 1 illustrates generally a conventional four-ring groove internal combustion engine piston, operating in an engine cylinder. The assembly 10 includes a piston 11 and an engine cylinder 12 with a bore 13, receiving the piston 11. The piston 11 has a head 14 with a ring band 15 having four peripheral ring grooves 16, 17, 18 and 19 therearound. The top ring groove 16 has a split solid cast iron compression -or fire piston ring 20 therein. The second ring groove 17 has a split solid second compression ring 21 somewhat wider than the ring 20. The third ring groove 18 carries a two-piece oil control'ring assembly 22. The fourth or bottom ring groove 19 carries a three-piece oil control ring assembly 23.

As shown in FIG. 2, the top compression or fire ring 20 has a main body 24 composed of cast iron, preferably nodular gray iron, with a carbon content of about 3% percent by weight. The outer periphery 25 of this ring is covered with a plasma jet applied zirconium oxide coating 26. I

As shown in FIG. 3, the second compression ring 21 has a main body 27 composed of the same type of cast iron as the body 24 of the ring 20. The outer periphery 28 of the body 27 is inclined upwardly and inwardly from the bottom edge of the ring, and a peripheral groove 29 is formed around this inclined periphery. The groove 29 is filled with a coating 26.

As shown in FIG. 4, the oil control ring assembly 22 in the third ring groove 18 is composed of a one-piece flexible channel ring 30 and a sheet-metal expander ring 31, having legs extending into the channel for expanding the ring 30. The ring 30 and the expander are more fully described in the Donald J. Mayhew et al. Pat. No. 3,281,156.

The one-piece control ring 30 has a pair of axially spaced, radially projecting beads 32. The peripheries of these-beads 32 are coated with the coating 26.

In FIG. 5, the oil control ring assembly 23 includes a resilient spacer-expander ring 33 supporting and expanding split thin rail rings 34. The assembly 33 is of the type disclosed in the Melvin W. Marien Pat. Nos. 3,133,341 and 3,133,739. The outer peripheries of the rail rings 34 are coated with the coating 26, according to this invention.

From the above description, it will be understood that the bearing faces of each of the compression and oil control rings 20, 21, 22 and 23 are coated with either one or the other coatings described in this invention. These bearing faces 26 ride on and sealingly engage the bore 13 of the engine cylinder 12, and the rings are compressed in the bore 13, so as to expand tightly against the bore wall, and maintain a good sealing sliding engagement therewith.

As shown in FIG. 6, the coatings 26 are applied on i the rings as for example on the grooved rings 21 by stacking a plurality of the rings on an arbor 35, with the rings compressed so that their split ends will be in near abutment. The arbor clamping the stack of rings in their closed, contracted position may be mounted in a lathe and the peripheries of the rings machined to form the grooves 29 therearound. The outer peripheries of the rings 21 on the arbor are then coated with the coatings 26 from a plasma jet spray gun 36. The gun 36 includes an insulated casing such as Nylon 37, from which projects a rear electrode 38, the projection of which is adjustably controlled by a screw knob 39. The front face of the casing receives a front electrode 40. The casing 37 and electrode 40 are hollow and waterjaeketed so that coolant may circulate therethrough from an inlet 41 to an outlet 42. Plasma jet gas if fed through an inlet 43 into the chamber provided by the casing 37 and the electrode 40 to flow around the electrode 38.

The front end of the electrode 40 provides a nozzle outlet 44 for the plasma flame and the ingredients to form the coating 26 are fed to this nozzle through a powder inlet 45, just in advance of the discharge outlet of the nozzle.

A plasma composed of ionized gas is produced by passing the plasma gas from the inlet 43 through an electric are established between the electrodes 38 and 40. This plasma gas is non-oxidizing and may be composed of nitrogen and hydrogen with argon, or helium as a carrier. The plasma flame in discharging the nozzle 44 draws the powder therewith by aspiration and subjects the powder ingredients to high temperatures. The jet stream carries the ingredient or ingredients into the bottom of the groove 29 of each piston ring and fills the groove.

It is greatly preferred that the zirconium oxide coatings be plasma jet applied in situ upon the bearing face of the piston ring as just noted. In the usual case the outer coatings are applied by coating the piston rings from a powder fed to a plasma jet stream.

In some instances it may be preferred to first apply a bond coat for the outer coating of zirconium oxide. Preferred bond coats of this type include both molybdenum and nickel-aluminide. However, in any event, the hardness of the layers of multi-layer coatings is found to be the same as if each of the coatings had been applied by themselves. It should therefore be understood, of course, that satisfactory bondings with cast iron are obtained directly with the zirconium oxide without the use of a separate bond-coating material.

A typical underlying coating of nickel and aluminum includes 80-95 percent by weight of nickel, with the remainder being aluminum.

The coatings of the invention are applied via a plasma jet spray technique.

The coatings here have excellent hardness. For example, the hardness of the zirconium oxide outer coating is a Vickers Hardness (DPl-l) of 1,000 and more often ranges between about 1,300 and 1,600.

It should be noted here that the zirconium oxide coating has excellent hardness and scuff-resistance as will be demonstrated hereinafter. Also, said coating may be ground utilizing conventional techniques.

The following examples illustrate typical conditions utilized in spraying the coatings of the invention upon piston rings. In each instance,'a plasma jet spray technique was utilized.

EXAMPLE I A zirconium oxide coating was plasma jet applied here by following the below variables with respect to the plasma jet technique.

Number of Guns 1 I arbor diameter.

It has also been noted that the particle distribution size of the zirconium oxide powder utilized in the plasma jet spray technique is important particularly to achieve proper tensile strength. If the powder is too coarse the resultant coating has reduced strength and is not porous enough to retain oil.

For best results, the zirconium oxide powder should have a particle distribution size of at least 50 percent by weight of less than 40 microns. Preferably at least percent of the zirconium oxide should have a particle distribution size less than about 40 microns.

A typically useful zirconia powder has the following sieve analysis:

TABLE I Size Range Fraction -'200 250 mesh 2.0 -250 350 mesh l5.4 325 mesh 50 microns 4.0 S 40 microns 34.1 40 30 microns l2.6 30 4- 25 microns 16.6 25 20 microns 10.1 20 15 microns 3.l l IO microns 2.1 l0 microns 0 in the following group of studies the zirconia coatings were analyzed after application to piston rings with respect to grinding characteristics, hardness, oxidation resistance and engine test 'to'obtain wear data.

EXAMPLE ii In this first series of tests, a piston ring was coated with a hard outer zirconium oxide coating and an underlying molybdenum coating. Such series of coatings could be ground using normal grinding practices.

EXAMPLE Ill The coatings of Example II were then tested for hardness. With respect to the zirconium oxide-molybdenum coating the outer zirconium oxide coating had a hardness of 1592 Vickers (DH-1). and the underlying molybdenum coating had a hardness of 922.

EXAMPLE IV The coatings of Example ll were then subjected to extensive heat treatment in order to indicate the degree of oxidation as measured by major color changes. The coatings, when heated at 750 F. for 100 hours did not indicate any oxidation.

With respect to the above coatings, no significant hardness changes were observed on anyof the coatings before and after heating to either 750 F. or l,000 F. for the 100 hour period.

EXAMPLE V Still further testing was carried out with respect to piston rings having a zirconium oxide coating. In a porosity test, the zirconium oxide coating had a porosity of -15 percent.

EXAMPLE Vi tions at each location. Measurements were taken of the cylinder both lengthwise and across at the five locations from the top of the cylinder bore as follows:

1. At top of ring travel approximately 2. 1 inch from top 3. 2 inches from top 4. 3 inches from top 5. 4 inches from top.

This procedure was then repeated after the test and the difference was calculated for each position.

The zirconium oxide coatings from a ring wear standpoint and a bore wear standpoint passed the above test,

' and in many instances were superior to conventional The zirconium oxide coatings on piston rings were also subjected to engine tests in a'Renault 70 mm test engine in order to determine wear characteristics and were found to be acceptable and in many cases superior to conventional piston ring coatings.

Specifically, both end clearance change and bore wear data were obtained. With respect to the end clearance change the following procedure was carried out. The rings were first confined in a precise diameter gauge. in order to avoid a change in end clearance (E. C.) due' to small changes in gauge diameter, the same gauge was used before and after the test. The end clearance between the two gap ends was then measured using a tool makers microscope with a calibrated lens system. Thereafter, the rings were installed and the engine run in a specific test schedule for the prescribed length of time. After the test was completed the rings were removed from the engine, any carbon accumulation carefully removed, and the above measurement repeated. The difference between the two measurements in end clearance then is a measurement of wear.

With respect to the bore wear test, each bore was measured before the test at five locations in two direcpiston ring coatings with respect to wear characteristics. Data are given in the following Table ll.

TABLE II Zirconium oxide coating Distance from Cylinder number top of cylinder 1 2 3 4 Top ring:

Before 023 022 023 024 After 02A .023 024 025 Average chan e .001 .001 .001 .001

2nd ring:

Before" .024 .024 v .023 .024 After- .027 026 02A. 027

Average change .003 I 002 001 003 Bore Woar Test Crosswis0 M; 2.7502 2.7503 2.7564 2.7558 Before 1 2. 7502 2. 7563 2. 7563 2. 7500 2 2. 7503 2. 7563 2. 7564 2. 7504 8 2. 7565 2. 7506 2. 7560 2. 7507 4 2. 7505 2. 7506 2. 7508 2.7567

Average 2. 7564 2. 7504 2. 7565 2. 7563 Crosswlse.... 2.750.5 1.7505 2. 7582 2.7501 After 1 2. 7564 2. 7503 2. 7562 2. 7502 2 2. 7562 2. 7560 2. 7561 2. 7503 3 2. 7502 2. 7560 2. 7562 2. 7503 4 2. 7557 2. 7558 2. 7500 2. 7500 Avora 2. 7508 2. 7507 2. 7505 2. 7508 Average changm. 0005 0003 0000 0005 Lengthwisc M. 2. 7507 23575377570 Beiorc 1 2.7565 2. 7568 2. 7568 2. 7504 2 2. 7505 2. 7506 2. 7567 2. 7565 3 2. 7565 2. 7560 2. 7566 2. 7567 4 2. 7560 2. 7564 2. 7505 2. 7564 Average 2. 7564 2. 7567 2. 7507 2. 7565 Lengthwise-. V; 2. 7586 2. 7583 2. 7584 2. 7584 After 1 2. 7558 2. 7568 2. 7500 2. 7554 2 2. 7557 2. 7563 2. 7562 2. 7558 3 2. 7559 2. 7504 2. 7564 2. 7562 4 2.7562 2. 7563 2.7562 2.7562

Average 2. 7564 I 2. 7568 2. 7566 2.7564 Average change .0000 0001 0001 0001 SUMMARY The presentinvention provides hard-faced piston rings having coatings of zirconium oxide. The rings of the invention are preferably coated utilizing a plasma jet technique wherein said coatings are formed in situ on the ring. in addition to excellent hardness the coatings also exhibit superior scuff-resistance. Also, they can be finished by grinding on conventional silicon carbide and aluminum oxide grinding wheels.

We claim as our invention:

1. A piston ring comprising a ferrous metal body, a porous scuff-resistant bearing coating therefor consisting essentially of zirconium oxide, and an underlying bond coat uniting said bearing coating to said metal body, said bond coat being a nickel aluminum alloy containing between and percent by weight of nickel and improving the adhesion of the zirconium oxide to the metal body.

2. A piston ring in accordance with claim 1 in which the zirconium oxide coating is formed by plasma jet 3. A piston ring in accordance with claim 2 in which at least 70 percent by weight of the zirconium oxide power has a particle size less than 40 microns.

4. A piston ring in accordance with claim 1 in which stream of zirconium oxide powder at least 50 percent 5 said coating has a Vickers Hardness (DH-1). of at least by weight of which has a particle size of less than 40 microns. 

1. A piston ring comprising a ferrous metal body, a porous scuff-resistant bearing coating therefor consisting essentially of zirconium oxide, and an underlying bond coat uniting said bearing coating to said metal body, said bond coat being a nickel aluminum alloy containing between 80 and 95 percent by weight of nickel and improving the adhesion of the zirconium oxide to the metal body.
 2. A piston ring in accordance with claim 1 in which the zirconium oxide coating is formed by plasma jet stream of zirconium oxide powder at least 50 percent by weight of which has a particle size of less than 40 microns.
 3. A piston ring in accordance with claim 2 in which at least 70 percent by weight of the zirconium oxide power has a particle size less than 40 microns.
 4. A piston ring in accordance with claim 1 in which said coating has a Vickers Hardness (DPH)40 of at least 1,000. 